linux-kernel - Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

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Date:	Wed, 14 Nov 2012 16:01:13 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	"Trond.Myklebust@...app.com" <Trond.Myklebust@...app.com>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...nvz.org" <devel@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v3] SUNRPC: set desired file system root before
 connecting local transports

On Mon, Nov 12, 2012 at 12:37:54PM +0400, Stanislav Kinsbursky wrote:
> 07.11.2012 22:33, J. Bruce Fields пишет:
> >On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
> >>On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> >>>On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> >>>>So you're worried that a bug in the nfs code could modify the root and
> >>>>then not restore it?
> >>>
> >>>At least the link you pointed to earlier never sets it back.
> >>
> >>This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> >>
> >>	+	get_fs_root(current->fs, &root);
> >>	+	set_fs_root(current->fs, &transport->root);
> >>	+
> >>	 	status = xs_local_finish_connecting(xprt, sock);
> >>	+
> >>	+	set_fs_root(current->fs, &root);
> >>	+	path_put(&root);
> >>
> >>>Instead
> >>>of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> >>>and not care about current->fs->root at all.
> >>
> >>The annoyance is that the lookup happens somewhere lower down in the
> >>networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
> >>need some new (internal) API.  We'd likely be the only user of that new
> >>API.
> >
> >So, if the only drawback is really just the risk of introducing a bug
> >that leaves the fs_root changed--the above seems simple enough for that
> >not to be a great risk, right?
> >
> 
> If we unshare rpciod fs struct (which is exported already), then we

I'm not sure what you mean by that.  Do workqueues actually have their
own dedicated set of associated tasks?  I thought all workqueues shared
a common pool of tasks these days.

> won't affect other kthreads by root swapping.
> But would be great to hear Trond's opinion about this approach.
> 
> Trond, could you tell us your feeling about all this?

I think it's often easier to get people to comment on an actual patch,
and this one would be quite short, so try that....

--b.
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